Factory Design Pattern in PHP, Is this correct?

I'm reading about Design Patterns in PHP, and, I'm skeptical of the code which I'd written to implement the Factory Design Pattern.

Does this code implement REAL Factory Design?

And, Do I need to use any interface here?

The code is:

class DBFactory 
{
   const MYSQL      =   1;
   const ORACLE     =   2;
   const SQLITE     =   3;

   private $objectTxt = null;

   function __construct($type) 
   {
       if ($type == self::MYSQL) {
           $this->objectTxt = 'MySQL Object'; 
           return ; //MySQL Object
       }

       else if ($type == self::ORACLE) 
       {
           $this->objectTxt = 'Oracle Object';
           return ; //Oracle Object
       }

       else if ($type == self::SQLITE)
       {
           $this->objectTxt = 'SQlite Object';
           return 'SQLite Object'; //SQLite Object           
       }
   }

   function __toString() {
        return $this->objectTxt;   
   }
}